The present invention relates to a wall plug device having metallic flat-blade electrical contact prongs.
Many electrical appliances use common line current which is supplied from electrical outlet sockets. The sockets accept a pair of flat blade-type prongs, each rectangular in cross section. The standard prongs are xc2xc inch wide, slightly less than {fraction (1/16)} inch thick, and almost xc2xe of an inch long. The two prongs are set xc2xd inch apart on centers. Usually a hole for a third, grounding prong is provided. The grounding prong is usually round in cross section, instead of rectangular.
If the appliance is electrically isolated from the line current, as by a transformer or double insulation, then the third grounding prong is not necessary and only the two flat prongs need be provided and inserted into the socket for electrical powering of the appliance. Often, when a transformer is provided, the transformer is packaged in a small plastic box or housing, with low voltage wires (from the low voltage side of the transformer) running from the box to the appliance proper. The transformer housing, rather than a separate jack or xe2x80x9cplugxe2x80x9d proper, then is placed directly against the socket when the prongs are inserted to power the appliance.
Such transformer housings are almost always molded of rubber or plastic insulating materials. The prongs need to be fastened to the box or housing in such a way that they are firmly held and that electrical contact paths can be made to them inside the housing, after which the (usually two) mating parts of the housing are closed.
In the prior art, a conventional method of fastening prongs to transformer and other plug-type housings has been to mold them directly into the plastic. The housing mold has been provided with passages for accepting the prongs and holding them during the plastic injection. Because the prongs must protrude on both the outside and the inside of the housing for electrical connection, both the male and female halves of the mold required passages.
Deficiencies in the prior art such as noted above have been overcome by the invention described in my issued U.S. Pat. No. 5,588,882, which is composed of a prong structure and method of attaching prongs to a housing to form a plug in a manner that reduces mold expense, cuts molding cycle time, and improves mechanical strength. Passages are provided in the molded housing that accept the prongs after the housing is molded and cooled. Each prong includes a body portion having the standard dimensions needed for insertion into a wall socket. At the point where the body is to meet the outer surface of the housing, the prong narrows at a shoulder to form a neck that is inserted into the passage of the housing and fits there snugly. At the end of the neck, adjacent the inner surface of the housing when the neck is fully inserted into the passage, is a twist portion, of reduced width, that separates the neck from the head of the prong. The twist portion lies between the neck and the head of the prong, and has, adjacent its width, opposing ledges or abutment surfaces on the neck and head. The head protrudes from the inner surface of the housing when the neck is fully inserted. After insertion, the head is twisted so that underside or abutment surfaces of the head, called the chin surfaces, rest against the inner surface of the housing.
Thus, after insertion and twisting, the prong is held longitudinally between the shoulder and the chin surfaces. The prong is also held against rocking and rotating about its length by the snug fit of the neck in the housing passage.
The present invention provides a novel prong structure and method offering improvements over the prior art described above
To this end, the invention provides a wall plug device for connecting an electrical appliance to a socket of a power supply system. The device is composed of: a housing having an outer surface and an inner surface and provided with two pairs of passages, each pair including a first passage and a second passage; and two electrical contact prongs, each having a main body portion and a connecting portion, the main body portion extending to a first end of the prong for making electrical contact with the socket outside the housing and the connecting portion extending to a second end of the prong that is remote from the first end. The connecting portion has an anchor element that extends through the first passage of a respective pair of passages and an electrical connection element that extends through the second passage of the respective pair of passages, and the anchor element is deformed from a first configuration in which the anchor element can be inserted through the first passage to a second configuration in which the anchor element is secured in the housing.